COLLATERALIZED AGREEMENTS AND FINANCINGS, Encumbered Assets (Details) - USD ($) $ in Millions	Sep. 30, 2023	Sep. 30, 2022
Had the right to deliver or repledge
Financial Instruments Owned and Pledged as Collateral [Line Items]
Financial instruments, owned, at fair value	$ 1,091	$ 1,276
Did not have the right to deliver or repledge
Financial Instruments Owned and Pledged as Collateral [Line Items]
Financial instruments, owned, at fair value	3,960	63
Asset pledged as collateral
Financial Instruments Owned and Pledged as Collateral [Line Items]
Financial instruments, owned, at fair value	10,166	8,800
Asset pledged as collateral | FHLB
Financial Instruments Owned and Pledged as Collateral [Line Items]
Financial instruments, owned, at fair value	9,400	8,009
Asset pledged as collateral | FRB
Financial Instruments Owned and Pledged as Collateral [Line Items]
Financial instruments, owned, at fair value	$ 766	$ 791